The present invention relates in general to radio pagers with silent alerting and, more particularly, to a very low-profile vibrator motor suitable for use with such pagers which exhibits substantial space saving characteristics, high reliability and completely silent operation.
Radio pagers with vibrator motors effecting selective silent alerting are of course known in the art. Instead of emitting an audible beep or tone upon the receipt of the proper selective call or page, the decoder circuits of these pagers activate an associated vibrator motor which alerts the wearer by tactile response that a call has in fact been received and decoded. Up to a few years ago, effecting the required silent alerting was readily accomplished by the vibrator motors then available in the market place. Such motors generally comprise a conventionalized structure having a cylindrical housing wherein a rotating shaft having a longitudinal axis of significant length to which an external but unbalanced counter weight was attached. By "significant length" it is meant that the rotating shaft is equal to or greater than the diameter of the motor. For example, reference is made to an early U.S. pat. No., 3,017,631 to Fink, et al., issuing in 1962. Further, two U.S. Pat. Nos. 3,618,070 and 3,623,064 issuing to Sholly Kagan in 1971 are also illustrative. U.S. Pat. No. 3,911,416 to Feder in 1975, assigned to the assignee of the present invention, is still another variation. See also FIG. 2 of the drawings herein as a typical example of such conventional vibrator motors. The motor 10 in FIG. 2 is included in a holder 12 which is mounted directly to the pager's printed circuit board 14. Included on the rotating shaft of the motor 10 is an eccentric counter weight 16.
Structures of this sort as above referenced may well be accommodated in pagers that have significant volume. That is simply not the case in present day pagers which have been steadily reducing in available volume while at the same time increasing in circuit complexity and included options, such as alphanumeric displays, memory devices for storing multiple calls, and the like. In short, space is being reduced and is at a decided premium for significant and desirable operational features such that vibrating motors presently in the art cannot be justified or accommodated. Moreover, with the vibrating motors mounted directly to the PC board, serious risk is engendered regarding optimum reliability standards because the vibration generated may well affect solder joints, fragile component parts, and the like on the PC board. Vibration levels for these motors may approach four G's or higher.
One other problem needs be addressed regarding these prior vibrator motor devices, namely, the usually unacceptable level of noise that is generated. When the silent alerting mode is selected by a radio pager user/wearer, it somewhat defeats the purpose if, in activating the silent alert, an audible whine or other sound is produced that may be heard by others in the vicinity. What is desired is an alerting arrangement which, when activated, is sensed only by the wearer of the device and not heard by others.
What is needed then is a miniaturized motor that may be easily and effectively accommodated into present day radio pagers, even those designated as "credit card" pagers, which will silently alert on the wearer of such pager without jeopardizing the reliability standards of the pager by the resulting vibration generated over the expected service life of the pager.